Granito Taquaral : evidências de um arco magmático orosiriano no sul do Cráton Amazônico na região de Corumbá - MS

Abstract

The Taquaral Granite comprises an intrusion of batholithic dimensions, located in the south of the Amazon Craton in Corumbá region - far west of the state of Mato Grosso do Sul, near the border between Brazil and Bolivia -, partially covered by sedimentary rocks of the Urucum, Tamengo, Bocaina and Pantanal formations and the Alluvial Deposits. Based on grain size, color, and composition along with detailed geological mapping, three petrographic facies are attributed to the rocks of Taquaral Granite: Medium to Coarse-grained Grey Facies, Coarse-grained Pink Facies and Fine-grained Pink Facies. The first facies is volumetrically dominant in the mapped body; characterized by leucocratic rocks, grey, inequigranular to equigranular medium-to-coarse grained, sometimes displaying a mylonitized texture and are classified as quartz-monzodiorite, granodiorite and monzogranite. The second facies consists of pink leucocratic rocks, inequigranular, coarse-grained, of quartz monzonite and monzogranite composition. In turn, the third facies consists of light-pink hololeucocratic rocks, equigranular to inequigranular, classified as fine-grained aplite dykes of monzogranitic to syenogranitic composition. Two different types of enclaves are locally found: one corresponds to a mafic xenolith; another is identified as felsic microgranular enclave. In the study area, diabase dikes are also found, always in direct contact with the granite. Two deformation phases are identified, one of ductile behaviour (F1) and another of brittle / ductile brittle behaviour (F2). Geochemical data indicate intermediate to acid composition for these rocks and suggest an arc environment, representing a medium to high-K calc-alkaline magmatism, metaluminous to peraluminous. SHRIMP U-Pb zircon ages of 1861 ± 5.3 Ma are attributed to crystallization. Sm-Nd whole rock analyses provided negative εNd(1.86 Ga) values (-1.48 and -1.28) and TDM model ages from 2.32 to 2.25 Ga indicating a Rhyacian crustal source. The results indicate that Taquaral Granite is an evidence of a magmatism developed in the Amoguijá Magmatic Arc in late Orosirian.